Transplant donors have either the B/x or A/A KIR genotype. During the current period of support we found that unrelated donors having B/x genotype confer significant relapse-free survival benefit to transplanted AML patients. By refining the analysis to separate B haplotype components, we defined a 'B-content score'as the best predictor of superior clinical outcomes. We propose that donor selection based on KIR, as well as HLA, genotyping should become standard practice for therapeutic transplants for AML. This Program will test the hypotheses that NK cells are of general importance in allogeneic transplantation and that variable NK cell receptor interactions influence clinical outcome. Conducting this Program is an international group of experts in NK cell biology and clinical transplantation. A focus for study is the thousands of transplants performed through the auspices of the NMDP, their associated blood and DNA samples, and the extensive high quality data on transplant outcome available through the CIBMTR. Project 1 (Peter Parham) will focus on the functions of characteristic B haplotype KIR, to determine the mechanisms by which they can influence transplant outcome. In Project 2, Jeffrey Miller proposes to evaluate NK cell education after adoptive transfer of haploidentical stem cells and subsequent reconstitution. He proposes a first human trial to investigate the capacity of hulL-15 to educate NK cells in vivo. In Project 3, Daniel Weisdorf will develop KIR typing for clinical use in selecting donors with KIR that improve transplant outcome. This method will also be used in the human trial of Project 2. Synergistic interaction between the Projects will take basic NK cell science from bench to bedside. Achieving this goal through better donor selection, understanding of NK cell regulation by KIR genetics and how best to exploit this knowledge clinically. As well as Administration and Clinical Research Support (Core A) and Biostatistics (Core B), the research will be supported by unique Informatics (Core C) and KIR genotyping (Core D) resources. This program will establish definitive roles for NK cells and their receptors in allogeneic transplantation and adoptive NK cell transfer. The program also promises to change practice of allogeneic transplantation, to the greater benefit of patients with advanced leukemia.